Microbiology Lecture 6: Neisseria

Questions and Answers

Which of the following outer membrane proteins prevents phagosome-lysosome fusion in neutrophils?

Por proteins (correct)

IgA1 protease

Opa proteins

Rmp (Protein iii)

How does the lipooligosaccharide (LOS) of gonococci differ from the lipopolysaccharide (LPS) of other Gram-negative bacteria?

It has longer O-antigen side chains

It has shorter O-antigen side chains

It is more toxic than LPS

It lacks the O-antigen side chains (correct)

What is the primary site of infection in women with gonococcal infection?

Vagina

Urethra

Uterine tubes

Endocervix (correct)

What is the consequence of gonococcal salpingitis in 20% of women?

Infertility Signup and view all the answers

What is the function of Rmp (Protein iii) in gonococci?

Associating with Por in the formation of pores Signup and view all the answers

How do Opa proteins contribute to the pathogenesis of gonococcal infection?

By mediating adhesion to host cell receptors Signup and view all the answers

What is the endotoxic effect of lipooligosaccharide (LOS) in gonococcal infection?

It is responsible for the toxicity in gonococcal infection Signup and view all the answers

What is the common consequence of urethral infection in men with gonococcal infection?

Painful urination Signup and view all the answers

What is the typical morphology of Neisseria species?

Gram-negative cocci in pairs Signup and view all the answers

What is the primary purpose of Kovac's oxidase test in identifying Neisseria?

To identify the presence of cytochrome oxidase Signup and view all the answers

What is the optimal growth condition for Neisseria species?

Aerobic conditions with complex organic substances Signup and view all the answers

What is the function of pili in Neisseria gonorrhoeae?

To increase resistance to phagocytosis Signup and view all the answers

What is the typical colony morphology of Neisseria species on enriched media?

Convex, glistening, elevated, and mucoid Signup and view all the answers

What is the effect of Kovac's reagent on Neisseria species?

It turns Neisseria into dark purple Signup and view all the answers

What is the typical size of Neisseria species?

0.8 µm in diameter Signup and view all the answers

What is the atmosphere required for the growth of Neisseria species?

5% CO2 and 95% O2 Signup and view all the answers

What is the primary route of transmission of gonococcal ophthalmia neonatorum?

Acquisition during passage through an infected birth canal Signup and view all the answers

What is the primary purpose of blood culture in the diagnosis of gonorrhea?

To check for the presence of the bacteria in systemic illness Signup and view all the answers

What is the advantage of using nucleic acid amplification tests in the diagnosis of gonorrhea?

It provides a more rapid result compared to culture Signup and view all the answers

What is the recommended treatment for uncomplicated gonorrhea?

Ceftriaxone (250 mg) given intramuscularly as a single dose Signup and view all the answers

What is the primary way to reduce the infection rate of gonorrhea?

All of the above Signup and view all the answers

What is the most common complication of meningococcemia?

Meningococcal meningitis Signup and view all the answers

What is the purpose of using a modified MTM with antibiotics in nasopharyngeal cultures?

To inhibit the growth of contaminants Signup and view all the answers

What type of medium is used to streak pus or mucus specimens for culture?

All of the above Signup and view all the answers

What is the purpose of Gram-stained smears in the diagnosis of meningococcemia?

To show the typical arrangement of Neisseria meningitidis within polymorphonuclear leukocytes Signup and view all the answers

What is the consequence of untreated gonococcal ophthalmia neonatorum?

Blindness Signup and view all the answers

What is the significance of antibacterial activity in serology?

It is used to detect the bactericidal activity of antibodies Signup and view all the answers

What is the recommended treatment for possible concomitant chlamydial infections?

Azithromycin (1 g) orally in a single dose Signup and view all the answers

What is the purpose of taking specimens of spinal fluid in the diagnosis of meningococcemia?

To perform smear, culture, and chemical determinations Signup and view all the answers

What is the significance of petechiae in meningococcemia?

They can be used to obtain specimens for smear and culture Signup and view all the answers

What is the primary purpose of applying 0.5% erythromycin ophthalmic ointment or 1% tetracycline ointment to the conjunctiva of newborns?

To prevent gonococcal ophthalmia neonatorum Signup and view all the answers

What is the unique characteristic of Neisseria meningitidis that distinguishes it from gonococci?

Utilization of maltose Signup and view all the answers

What is the percentage of healthy individuals that can be asymptomatically colonized by Neisseria meningitidis?

5-10% Signup and view all the answers

What is the primary role of pili and outer membrane proteins in Neisseria meningitidis?

Playing a key role in colonization as adhesins Signup and view all the answers

What is the function of lipooligosaccaride in Neisseria meningitidis?

Causing fever and septic shock in systemic infection Signup and view all the answers

Which of the following serogroups of Neisseria meningitidis are associated with disease in humans?

A, B, C, X, Y, and W-135 Signup and view all the answers

What is the mechanism by which Neisseria meningitidis is transmitted from one person to another?

Through respiratory droplets Signup and view all the answers

What is the role of capsular polysaccharide in Neisseria meningitidis?

Conferring resistance to serum bactericidal activity Signup and view all the answers

Study Notes

Characteristics of Neisseria Species

Neisseria species are Gram-negative cocci, usually occurring in pairs to form diplococci
There are two medically important species: Neisseria gonorrhoeae (gonococci) and Neisseria meningitidis (meningococci)
Other species are members of normal human respiratory tract microbiota, and either rarely or never cause disease

Typical Neisseria Characteristics

Gram-negative, non-motile, kidney-shaped diplococcus
Bacterial cells are about 0.8 µm in diameter
Grow best under aerobic conditions
Oxidize carbohydrates, producing acid but not gas
Fastidious, growing on media containing complex organic substances such as heated blood, hemin, and animal proteins
Require an atmosphere containing 5% CO2
Sensitive to desiccation, moist heat, sunlight, and many different disinfectants

Identification Tests

Kovac's oxidase test: determines the presence of cytochrome oxidase, which causes Neisseria to turn dark purple when treated with Kovac's reagent
Other identification tests: Gram-stained smear, culture, coagglutination, immunofluorescence staining, and further laboratory tests

Virulence Factors of Neisseria

Pili: hair-like appendages that enhance attachment to host cells and resistance to phagocytosis
Outer membrane proteins:
- Por proteins: affect intracellular killing of gonococci within neutrophils and confer resistance to bactericidal activity of normal human serum
- Opa proteins: mediate adhesion of gonococci to host cell receptors
- Rmp (Protein iii): associates with Por in the formation of pores in the cell surface
IgA1 protease: inactivates IgA1 antibodies, which are the main mucosal antibody of humans
Lipooligosaccharide (endotoxin): differs from lipopolysaccharide (LPS) of other Gram-negative bacteria, lacks long O-antigen side chains, and is responsible for endotoxic effects in gonococcal infection

Pathogenesis and Transmission of Neisseria

Transmission:
- Neisseria gonorrhoeae: sexual contact, birth (infection of newborns during passage through an infected birth canal)
- Neisseria meningitidis: respiratory droplets, bacteria can colonize around 5-10% of healthy individuals asymptomatically
Pathogenesis:
- Neisseria gonorrhoeae: attacks mucous membranes of different sites of the body, resulting in acute suppuration, tissue invasion, chronic inflammation, and fibrosis
- Neisseria meningitidis: colonizes the nasopharynx, reaches the bloodstream, and spreads to the meninges, causing bacteremia, meningococcemia, and meningitis

Diagnosis of Neisseria Infections

Neisseria gonorrhoeae:
- Specimens: pus and secretions from urethra, cervix, rectum, conjunctiva, throat, or synovial fluid
- Smears: Gram-stained smears of urethral or endocervical exudates reveal many diplococci within pus cells
- Culture: pus or mucus specimens can be streaked onto enriched or selective medium, incubated at 37°C in 5% CO2
Neisseria meningitidis:
- Specimens: blood, spinal fluid, nasopharyngeal swab cultures
- Smears: Gram-stained smears of the sediment of centrifuged spinal fluid or petechial aspirate often show typical neisseriae within polymorphonuclear leukocytes or extracellularly
- Culture: blood and cerebrospinal fluid specimens are plated onto agar culture media, modified MTM with antibiotics for nasopharyngeal cultures
- Serology: antibodies against capsular polysaccharides can be used as a detection test, detected by latex agglutination or hemagglutination tests or by bactericidal activity

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Description

This lecture covers the characteristics and diagnosis of diseases caused by Neisseria species, including Neisseria gonorrhoeae and Neisseria meningitidis.